Integrated circuit for controlling charging, charging device using the integrated circuit, and method for detecting connection of secondary battery

ABSTRACT

An integrated circuit for charging a secondary battery including a charge current detection circuit detecting a charge current output from a charging transistor, and generating a signal including the charge current information; a voltage comparison circuit comparing a voltage of the battery with one or more predetermined voltages, and generating a signal including the voltage comparison information; and a charge controlling circuit controlling the charging transistor according to information on the voltage of the battery and the signals output from the charge current detection circuit and the voltage comparison circuit such that the charging transistor performs constant current charging or constant voltage charging, wherein the charge controlling circuit stops applying a charge current for a predetermined time in the beginning of charging, and judges that the battery is abnormally connected when the voltage of the battery becomes less than a predetermined voltage within the predetermined time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/701,434, filed on Feb. 2, 2007 now U.S. Pat. No. 7,479,765, which isbased on and claims priority to Japanese Patent Application No.2006-05269, filed on Feb. 28, 2006, the disclosures of each of which arehereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an integrated circuit for controllingcharging of a secondary battery, and more particularly to an integratedcircuit for determining whether a secondary battery is set in a chargingdevice on the basis of the charging state of the secondary battery. Inaddition, the present invention also relates to a charging device usingthe integrated circuit, and a method for determining whether a secondarybattery is set in a charging device.

2. Discussion of the Background

Until now, the following methods have been used for determining whethera secondary battery is set in a charging device.

(1) methods using a switch which achieves an ON state when a secondarybattery is set in a charging device while achieving an OFF state when nosecondary battery is set (disclosed in, for example, publishedunexamined Japanese patent application No. (hereinafter referred to asJP-A) 10-285812); and(2) methods in which a current is applied to a temperature detectionthermistor, which is included in a battery pack, to check the voltage ofthe terminal of the thermistor, resulting in determination whether ornot a battery is present (disclosed in, for example, Japanese patent No.(hereinafter referred to as JP) 2927354 (i.e., JP-A 01-186126).

The first-mentioned methods have a drawback in that a switch has to beprovided, thereby increasing the size and costs of the device. Thesecond-mentioned methods have drawbacks in that the methods cannot beused for batteries having no thermistor; and it is necessary to connecta terminal with the thermistor, thereby increasing the size and costs ofthe device. In addition, although the first-mentioned andsecond-mentioned methods can determine whether a battery is set in acharging device but cannot determine whether a battery is electricallyconnected with a terminal of the charging device.

In addition, the following methods, which do not use a switch or athermistor, have been proposed (for example, JP 3203538 (i.e., JP-A08-168188):

(3) methods in which a charge current is applied to a battery when avoltage not less than a predetermined voltage is detected betweenterminals of a charging device connected with the battery, wherein whenthe charge current is greater than a predetermined threshold current ina full charge state, it is judged that the battery is connected, andwhen the charge current is less than the threshold current, it is judgedthat the battery is fully charged. In addition, two additional thresholdcurrents are set near the above-mentioned threshold current. When thetime needed for changing the current from one of the additionalthreshold currents to the other is not less than a predetermined time,it is judged that the battery is fully charged. Further, when the timeis less than the predetermined time, it is judged that the battery isdetached from the charging device.

Further, the following methods, which do not use a switch or athermistor, have been proposed (for example, JP-A 10-225001):

(4) methods which perform intermittent charging while measuring thevoltage between terminals connected with a battery and the chargecurrent in a charging process, wherein whether or not a battery isconnected is determined on the basis of the results.

However, the third-mentioned methods have a drawback in that anover-discharge battery cannot be charged. Specifically, when charging isperformed on an over-discharge battery while applying a large currentthereto, a serious accident such as heat generation of heat or fire mayoccur, and therefore it is necessary to charge the battery whileapplying a small current until the battery has a predetermined voltage.Therefore, the threshold voltage which is used for judging whether ornot a battery is present has to be set so as to be greater than thevoltage of an over-discharge battery. In addition, the method in whichtwo additional threshold currents are set near the above-mentionedthreshold current (i.e., full-charge current) to determine whether abattery is connected and the battery is fully charged has a drawback inthat the scale of the circuit increases.

It is necessary for the fourth-mentioned methods to perform intermittentcharging in addition to general constant current − constant voltagecharging, and therefore an intermittent charging device has to beprovided. Accordingly, the methods have a drawback in that the size andcosts of the charging device increase.

Because of these reasons, a need exists for an integrated circuit (and acharging device), which can determine whether a secondary battery iscorrectly connected with a charging device while having a small size andlow costs.

SUMMARY OF THE INVENTION

As one aspect of the present invention, an integrated circuit forcharging a secondary battery via a charging transistor is provided whichincludes a charge current detection circuit which detects a chargecurrent output from the charging transistor, and generates and outputs asignal including the charge current information; a voltage comparisoncircuit which compares the voltage of the secondary battery with one ormore predetermined voltages, and generates and outputs a signalincluding the voltage comparison information; and a charge controllingcircuit which controls the charging transistor according to informationon the voltage of the secondary battery and the signals output from thecharge current detection circuit and the voltage comparison circuit suchthat the charging transistor performs constant current charging in whicha predetermined current is output or constant voltage charging in whicha charge current is output so that the secondary battery has apredetermined voltage. The charge controlling circuit stops applying acharge current for a predetermined time T1 in the beginning of chargingof the secondary battery. When the voltage comparison circuit detectsthat the voltage of the secondary battery becomes less than apredetermined voltage V1 within the predetermined time T1, the chargecontrolling circuit judges that the secondary battery is abnormallyconnected and performs an abnormality correction treatment (such asstopping of application of charge current).

Alternatively, in the integrated circuit, when the voltage comparisoncircuit detects that the voltage of the secondary battery becomes notless than a predetermined voltage V2, the charge controlling circuitstops applying a charge current for a predetermined time T2, and inaddition when the voltage comparison circuit detects that the voltage ofthe secondary battery becomes less than a predetermined voltage V2− lessthan the voltage V2 within the time T2, the charge controlling circuitjudges that the secondary battery is abnormally connected and performsan abnormality correction treatment.

Alternatively, in the integrated circuit, when the charge currentdetection circuit detects that the charge current applied to thesecondary battery becomes less than a predetermined current i2, andfurther detects that the charge current becomes less than apredetermined current i1 less than the current i2 within a predeterminedtime T4, the charge controlling circuit judges that the secondarybattery is abnormally connected and performs an abnormality correctiontreatment.

As another aspect of the present invention, a charging device forperforming a constant current charging or a constant voltage charging toa secondary battery is provided which includes a charging transistor forcontrolling application of charge current to the secondary battery; anda charge controlling integrated circuit for controlling the chargingtransistor according to the information on the charge current applied tothe secondary battery and the voltage of the secondary battery, whereinthe charge controlling integrated circuit is the integrated circuitmentioned above.

As yet another aspect of the present invention, a method for determiningwhether a secondary battery is connected is provided which includesapplying a charge current to a secondary battery through a chargingtransistor; stopping applying a charge current for the predeterminedtime T1 in the beginning of the charging operation while checking thevoltage of the secondary battery within the time T1; and performing anabnormality correction treatment when the voltage of the secondarybattery becomes less than the predetermined voltage V1 within the timeT1.

Alternatively, a method for determining whether a secondary battery isconnected is provided which includes applying a charge current to asecondary battery through a charging transistor; checking the voltage ofthe secondary battery; stopping applying a charge current for thepredetermined time T2 when the voltage of the secondary battery becomesnot less than the predetermined voltage V2; and performing anabnormality correction treatment when the voltage of the secondarybattery becomes less than the predetermined voltage V2− less than thevoltage V2 within the time T2.

Alternatively, a method for determining whether a secondary battery isconnected is provided which includes applying a charge current to asecondary battery through a charging transistor; checking the currentapplied to the secondary battery for the predetermined time T4 when thecurrent becomes less than the predetermined current i2; and performingan abnormality correction treatment when the current is less than thepredetermined current i1 less than the current i2 within thepredetermined time T4.

These and other objects, features and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an example embodiment of thecharging device of the present invention;

FIG. 2 is a flowchart illustrating the operations of the charging deviceillustrated in FIG. 1;

FIG. 3 is a graph illustrating the relationship between the chargecurrent (ich) and the voltage (Vb) of the battery in the charging deviceillustrated in FIG. 1;

FIG. 4 is a schematic view illustrating another example embodiment ofthe charging device of the present invention; and

FIG. 5 a flowchart illustrating the operations of the charging deviceillustrated in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an integrated circuit for controllingcharging of a secondary battery, which is used for a charging device andwhich applies a charge current to the secondary battery through acharging transistor to charge the secondary battery, wherein theintegrated circuit controls the operation of the charging transistor.

In the first integrated circuit, the integrated circuit includes acharge current detection circuit which detects the charge current outputfrom the charging transistor, and generates and outputs a signalincluding the charge current information; a voltage comparison circuitwhich compares the voltage of the secondary battery with one or morepredetermined voltages, and generates and outputs a signal including thevoltage comparison information; and a charge controlling circuit whichcontrols the charging transistor according to information on the voltageof the secondary battery and the signals output from the charge currentdetection circuit and the voltage comparison circuit such that thecharging transistor performs constant current charging in which apredetermined current is output or constant voltage charging in which acharge current is output so that the secondary battery has apredetermined charge voltage. In this integrated circuit, the chargecontrolling circuit stops applying a charge current for a predeterminedtime T1 in the beginning of charging of the secondary battery. When thevoltage comparison circuit detects that the voltage of the secondarybattery becomes less than a predetermined voltage V1 within thepredetermined time T1, the charge controlling circuit judges that thesecondary battery is abnormally connected and performs an abnormalitycorrection treatment (such as stopping of application of chargecurrent).

In addition, when the voltage comparison circuit detects that thevoltage of the secondary battery becomes not less than a predeterminedvoltage V2 greater than the voltage V11 the charge controlling circuitstops applying a charge current for a predetermined time T2. In thisregard, when the voltage comparison circuit detects that the voltage ofthe secondary battery becomes less than a predetermined voltage V2−,which is greater than the voltage V1 and less than the voltage V2,within the time T2, the charge controlling circuit judges that thesecondary battery is abnormally connected and performs an abnormalitycorrection treatment.

Further, when the charge current detection circuit detects that thecharge current applied to the secondary battery becomes less than apredetermined current i2 and further detects that the charge currentbecomes less than a predetermined current i1 less than the current i2within a predetermined time T4, the charge controlling circuit judgesthat the secondary battery is abnormally connected and performs anabnormality correction treatment.

Furthermore, when the voltage comparison circuit detects that thevoltage of the secondary battery becomes not less than a predeterminedvoltage V3 greater than the voltage V2, the charge controlling circuitstops applying a charge current for a predetermined time T3. In thisregard, when the voltage comparison circuit detects that the voltage ofthe secondary battery becomes less than a predetermined voltage V3−,which is greater than the voltage V2 and less than the voltage V3,within the time T3, the charge controlling circuit judges that thesecondary battery is abnormally connected and performs an abnormalitycorrection treatment.

Alternatively, another integrated circuit (second integrated circuit) isprovided which includes the charge current detection circuit; thevoltage comparison circuit; and the charge controlling circuit, whereinwhen the voltage comparison circuit detects that the voltage of thesecondary battery becomes not less than the predetermined voltage V2,the charge controlling circuit stops applying a charge current to thesecondary battery for the time T2, and wherein when the voltagecomparison circuit detects that the voltage of the secondary batterybecomes less than the voltage V2− less than the voltage V2 within thetime T2, the charge controlling circuit judges that the secondarybattery is abnormally connected and performs an abnormality correctiontreatment.

In this regard, when the charge current detection circuit detects thatthe charge current applied to the secondary battery becomes less thanthe current i2 and further detects that the charge current becomes lessthan the current i1 less than the current i2 within the predeterminedtime T4, the charge controlling circuit judges that the secondarybattery is abnormally connected and performs an abnormality correctiontreatment.

In this integrated circuit, when the voltage comparison circuit detectsthat the voltage of the secondary battery becomes not less than thepredetermined voltage V3 greater than the voltage V2, the chargecontrolling circuit stops applying a charge current for thepredetermined time T3. In this regard, when the voltage comparisoncircuit detects that the voltage of the secondary battery becomes lessthan the predetermined voltage V3−, which is greater than the voltage V2and less than the voltage V3, within the time T3, the charge controllingcircuit judges that the secondary battery is abnormally connected andperforms an abnormality correction treatment.

Alternatively, another integrated circuit (third integrated circuit) isprovided which includes the charge current detection circuit; thevoltage comparison circuit; and the charge controlling circuit, whereinwhen the charge current detection circuit detects that the chargecurrent applied to the secondary battery becomes less than the currenti2 and further detects that the charge current becomes less than thecurrent i1 less than the current i2 within the time T4, the chargecontrolling circuit judges that the secondary battery is abnormallyconnected and performs an abnormality correction treatment.

In the first integrated circuit, the voltage comparison circuit caninclude a first comparator comparing the voltage of the secondarybattery with the voltage V1 and generating and outputting a first signalS1 including the comparison information to the charge controllingcircuit. The voltage comparison circuit can further include a secondcomparator comparing the voltage of the secondary battery with thevoltage V2 and generating and outputting a second signal S2 includingthe comparison information to the charge controlling circuit. In thisregard, the second comparator includes a first hysteresis controlledaccording to a control signal input from the charge controlling circuit,wherein the voltage V2− is the difference between the voltage V2 and thefirst hysteresis.

The voltage comparison circuit can further include a third comparatorcomparing the voltage of the secondary battery with the voltage V3 andgenerating and outputting a third signal S3 including the comparisoninformation to the charge controlling circuit. In this regard, the thirdcomparator includes a second hysteresis controlled according to an inputcontrol signal input from the charge controlling circuit, wherein thevoltage V3− is the difference between the voltage V3 and the secondhysteresis.

In the second integrated circuit, the voltage comparison circuit caninclude the second comparator or a combination of the second comparatorand the third comparator.

The first to third integrated circuits can further include an inputterminal which is connected with the secondary battery and to which thevoltage of the secondary battery is input; and a current source which isconnected with the input terminal while being controlled according tothe control signals input from the charge controlling circuit, whereinthe charge controlling circuit controls drive of the current sourceaccording to an external control signal for controlling a consumptioncurrent of a load to which the secondary battery applies a power. Inthis regard, the charge controlling circuit allows the current source tooperate when the external signal is a signal to reduce the consumptioncurrent is input while the charge current is not supplied to thesecondary battery. In addition, when input of such an external signal isstopped, the charge controlling circuit stops the operation of thecurrent source.

When the charge controlling circuit judges that the secondary battery isabnormally connected, the charge controlling circuit preferably stopsapplying a charge current to the secondary battery.

As another aspect of the present invention, a charging device forperforming constant current charging or constant voltage charging on asecondary battery is provided which includes a charging transistor forcontrolling application of charge current to the secondary battery; anda charge controlling integrated circuit for controlling the chargingtransistor according to the information on the charge current applied tothe secondary battery and the voltage of the secondary battery, whereinthe charge controlling integrated circuit is the above-mentioned first,second or third integrated circuit.

As yet another aspect of the present invention, a method for determiningwhether a secondary battery is connected is provided which includesapplying a charge current to a secondary battery through a chargingtransistor; and stopping applying a charge current for the predeterminedtime T1 in the beginning of the charging operation while checking thevoltage of the secondary battery within the time T1. When the voltage ofthe secondary battery becomes less than the predetermined voltage V1within the time T1, it is judged that the secondary battery isabnormally connected and the abnormality correction treatment isperformed.

When the voltage of the secondary battery becomes less than thepredetermined voltage V2 greater than the voltage V1, the method furtherincludes stopping applying a charge current for the predetermined timeT2 while checking the voltage of the secondary battery within the timeT2. In this regard, when the voltage of the second battery becomes lessthan the predetermined voltage V2−, which is greater than the voltage V1and less than the voltage V2, within the time T2, it is judged that thesecondary battery is abnormally connected, and the abnormalitycorrection treatment is performed.

In addition, the charge current may be checked. When the charge currentbecomes less than the predetermined current i2, the current is checkedfor the predetermined time T4. When the current becomes less than thecurrent i1 less than the current i2 within the time T4, it is judgedthat the secondary battery is abnormally connected, and the abnormalitycorrection treatment is performed.

Alternatively, a method for determining whether a secondary battery isconnected is provided which includes applying a charge current to asecondary battery through a charging transistor; checking the voltage ofthe secondary battery; and stopping applying a charge current for thepredetermined time T2 when the voltage of the secondary battery becomesnot less than the voltage V2. When the voltage of the secondary batterybecomes less than the predetermined voltage V2− less than the voltage V2within the time T2, it is judged that the secondary battery isabnormally connected, and the abnormality correction treatment isperformed.

In this regard, when the charge current becomes less than thepredetermined current i2, the current is checked for the predeterminedtime T4. When the current becomes less than the predetermined current i1less than the current i2 within the time T4, it is judged that thesecondary battery is abnormally connected, and the abnormalitycorrection treatment is performed.

Further, when the voltage of the secondary battery becomes not less thanthe predetermined voltage V3, the charge current to the secondarybattery is stopped for the predetermined time T3. When the voltagebecomes less than the predetermined voltage V3− greater than the voltageV2 and less than the voltage V3 within the time T3, it is judged thatthe secondary battery is abnormally connected, and the abnormalitycorrection treatment is performed.

Alternatively, a method for determining whether a secondary battery isconnected is provided which includes applying a charge current to asecondary battery through a charging transistor; and checking thecurrent of the secondary battery. When the current becomes less than thepredetermined current i2, the current is measured for the predeterminedtime T4. When the current becomes less than the predetermined current i1less than the current i2 within the time T4, it is judged that thesecondary battery is abnormally connected, and the abnormalitycorrection treatment is performed.

When it is judged that the secondary battery is abnormally connected, itis preferable to stop application of the charge current to the secondarybattery.

Next, the present invention will be explained in detail by reference todrawings.

First Example Embodiment

FIG. 1 is a schematic view illustrating an example embodiment of thecharging device of the present invention for charging a secondarybattery.

Referring to FIG. 1, a charging device 1 has a DC power source 5 such asAC adaptors and performs constant current charging or constant voltagecharging on a secondary battery 6 (hereinafter referred to as a battery)such as lithium ion batteries. The battery 6 is connected with a load 7and applies an electric power to the load 7.

The charging device 1 includes a power transistor Q1 for applying acurrent to the battery 6 according to a signal input to a base thereofto charge the battery, wherein the power transistor includes a PMOStransistor; and a resistor R1 configured to detect a current ich appliedby the power transistor Q1 to the battery 6. In addition, the chargingdevice 1 further includes a diode D1 configured to prevent backflow ofcurrent from the battery 6 to the DC power source 5; and a chargecontrolling circuit 2 configured to control the operation of the powertransistor Q1 so as to perform constant current charging or constantvoltage charging on the battery 6 according to information on a voltageVb of the battery 6 and the charge current ich, which can be determinedfrom the voltage of both the ends of the resistor R1.

The charge controlling circuit 2 is integrated in an IC, and includes aterminal P1 connected with the DC power source; a terminal P2 foroutputting a charge controlling signal; a first current detectionterminal P3; a second current detection terminal P4; and terminals P5and P6 connected with the battery 6, wherein the terminal P6 isgrounded. The battery 6 has battery terminals B+ and B−. The batteryterminal B+, which is connected with a positive electrode of the battery6, is connected with the terminal P5, and the battery terminal B−, whichis connected with a negative electrode of the battery 6, is connectedwith the terminal P6.

In addition, the charge controlling circuit 2 includes a power voltagedetection circuit 11 for determining whether a power is applied from theDC power source 5; a charge current controlling circuit 12 forcontrolling the operation of the power transistor Q1 according to theinput control signal; a charge current detection circuit 13 fordetermining the charge current ich from the voltage difference betweenthe terminals of the resistor R1.

Further, the charge controlling circuit 2 includes a reference voltagegenerating circuit 14 configured to generate and output a predeterminedreference voltage Vr; a comparator 15; comparators 16 and 17 each havinga hysteresis corresponding to the input control signal; resistorsR11-R14; and a controlling circuit 18 configured to control theoperation of the charge current controlling circuit 12 and thehysteresis of each of the comparators 16 and 17.

In this regard, the power transistor Q1 serves as the chargingtransistor, and the charge controlling circuit 2 serves as theintegrated circuit for controlling charging of a secondary battery. Inaddition, the reference voltage generation circuit 14, and comparators15-17, resistors R11-R14 constitute the voltage comparison circuit.Further, the charge current controlling circuit 12 and the controllingcircuit 18 constitute the charge controlling circuit. Furthermore, thecomparators 15, 16 and 17 are the first, second and third comparators,respectively.

The supply voltage Vdd applied by the DC power source 5 is input to thepower voltage detection circuit 11 via the terminal P1 while input tothe source of the power transistor Q1. The gate of the power transistorQ1 is connected with the charge current controlling circuit 12 via theterminal P2. The power voltage detection circuit 11 outputs apredetermined signal Sv to the controlling circuit 18 when the voltageof the terminal P1 becomes not less than a predetermined voltage toinform that a power is supplied from the DC power source 5. The chargecurrent controlling circuit 12 outputs a charge controlling signal tothe gate of the power transistor Q1 via the terminal P2 upon receptionof a control signal Sc from the controlling circuit 18 to control thecharge current ich.

The drain of the power transistor Q1 is connected with an anode of thediode D1 via the resistor R1. The cathode of the diode D1 is connectedwith each of the battery terminal B+ and the terminal P5. The drain ofthe power transistor Q1 is connected with the first current detectionterminal P3. The resistor R1 is connected with the first currentdetection terminal P3 and the second current detection terminal P4. Thecharge current detection circuit 13 determines the current ich from thevoltage difference between both the ends of the resistor R1 (i.e., thedifference between the voltage applied to the first current detectionterminal P3 and the voltage applied to the second current detectionterminal P4), and outputs a signal Si including the detected currentinformation to the controlling circuit 18.

The resistors R14, R13, R12 and R11 are serially connected between thereference voltage Vr output from the reference voltage generationcircuit 14 and the ground voltage. A first voltage V1, which is thevoltage at the connection point between the resistors R11 and R12, isinput to an inverting input terminal of the comparator 15. A secondvoltage V2, which is the voltage at the connection point between theresistors R12 and R13, is input to an inverting input terminal of thecomparator 16. A third voltage V3, which is the voltage at theconnection point between the resistors R13 and R14, is input to aninverting input terminal of the comparator 17. Each of a first voltagedetection signal S1 which is output from the comparator 15, a secondvoltage detection signal S2 which is output from the comparator 16, anda third voltage detection signal S3 which is output from the comparator17, is output to the controlling circuit 18.

In addition, the controlling circuit 18 inputs a first control signalSh1 for controlling the hysteresis of the comparator 16 and a secondcontrol signal Sh2 for controlling the hysteresis of the comparator 17to the comparator 16 and the comparator 17, respectively.

The comparator 15 compares the battery voltage Vb, which is the voltageat the terminal P5, with the first voltage V1. When the battery voltageVb becomes not less than the first voltage V1, the first voltagedetection signal S1 output from the comparator 15 is changed from a lowlevel to a high level. In contrast, when the battery voltage Vb becomesless than the first voltage V1, the first voltage detection signal S1 ischanged from a high level to a low level.

The comparator 16 compares the battery voltage Vb with the secondvoltage V2. When Vb is not less than V2, the second voltage detectionsignal S2 output from the comparator 16 is changed from a low level to ahigh level. When Vb is less than V2−, which is obtained by subtractingthe hysteresis voltage of the comparator 16 from the second voltage V2,the second voltage detection signal S2 output from the comparator 16 ischanged from a high level to a low level. The comparator 16 has an inputterminal, through which the first control signal Sh1 is input from thecontrolling circuit 18, to set the hysteresis voltage to a desired valueaccording to the control signal Sh1.

The comparator 17 compares the battery voltage Vb with the third voltageV3. When Vb is not less than V3, the third voltage detection signal S3output from the comparator 17 is changed from a low level to a highlevel. When Vb is less than V3−, which is obtained by subtracting thehysteresis voltage of the comparator 17 from the third voltage V3, thethird voltage detection signal S3 output from the comparator 17 ischanged from a high level to a low level. The comparator 17 has an inputterminal, through which the second control signal Sh2 is input from thecontrolling circuit 18, to set the hysteresis voltage to a desired valueaccording to the control signal Sh2.

The controlling circuit 18 is constituted of a logic circuit, anddetermines the charging mode on the basis of the output signal Sv outputfrom the power voltage detection circuit 11, the output signal Si outputfrom the charge current detection circuit 13, and the first, second andthird voltage detection signals S1, S2 and S3 output from thecomparators 15, 16 and 17, respectively. In addition, the controllingcircuit 18 determines whether or not charging is performed, and controlsthe charge current, and the charge voltage via the charge currentcontrolling circuit 12 using the control signal Sc.

FIG. 2 is a flowchart of the operations of the charging device 1illustrated in FIG. 1. FIG. 3 is a graph illustrating change of thecharge current ich and the battery voltage Vb with time in the chargingdevice illustrated in FIG. 1. The operations of the charging deviceillustrated in FIG. 1 will be explained by reference to FIGS. 2 and 3.

At first, the connection confirmation operation of the secondary batteryin the beginning of the charging operation will be explained.

Referring to FIG. 2, when the DC power source 5 is connected with thecharge controlling circuit 2 in step S1, the controlling circuit 18allows the charge current controlling circuit 12 to perform a resetoperation, i.e., to turnoff the power transistor Q1 so as to have ashutoff state, in step S2. In step S3, the power voltage detectioncircuit 11 checks the power voltage Vdd applied from the DC powerconnection terminal P1.

When the power voltage Vdd is less than a predetermined voltage in stepS3, the operation returns to step S2. When the power voltage Vdd is notless than the predetermined voltage in step S3, the controlling circuit18 allows the charge current controlling circuit 12 to turn off thepower transistor Q1 so as to have a shutoff state for a predeterminedcharge start waiting time T1 (step S4), resulting in stopping applyingthe charge current ich. Then the controlling circuit 18 checks thebattery voltage Vb on the basis of the first, second and third voltagedetection signals S1, S2 and S3 (step S5).

When the battery voltage Vb is less than the first voltage V1 in stepS5, the operation proceeds to step S22, in which the controlling circuit18 judges that the battery 6 is not connected or the battery 6 isabnormal. In this case, the controlling circuit 18 continuously allowsthe charge current controlling circuit 12 to turn off the powertransistor Q1 so as to have a shutoff state after the predeterminedcharge start waiting time T1, resulting in stopping of the chargecurrent ich (i.e., stopping of charging of the battery 6), followed byre-execution of step S5. When a voltage not less than the first voltageV1 is input to the battery connection terminal P5 (when a normalsecondary battery is connected, the voltage is not less than the firstvoltage V1), the first voltage detection signal S1 output from thecomparator 15 is on a high level. When the battery voltage Vb is notless than the first voltage V1 and less than the voltage V2− in step 5,the operation proceeds to step S6, in which the controlling circuit 18allows the charge current controlling circuit 12 to perform apreliminary charge mode operation.

In the preliminary charging mode operation, charging is performed whileflowing a relatively small amount of current of tens of milliamp untilthe battery voltage reaches a predetermined voltage. This is becausewhen charging is performed on a lithium-ion battery in an over-dischargestate while flowing a large amount of current, a problem such asgeneration of heat or fire may occur. In FIG. 3, a character “i1”denotes the charge current in the preliminary charging.

When the battery voltage Vb is not less than the voltage V2 in step S5,the output signal S2 output from the comparator 16 is changed from a lowlevel to a high level, and the operation proceeds to step S1 in whichcharging is performed in a constant current charging mode. In thisregard, the voltage V1 is set to a minimum voltage above which thepreliminary charging can be performed, and the second voltage V2 is setto a minimum voltage above which rapid charging flowing a large amountof current can be performed.

The charge start waiting time T1 is an extremely short time on the orderof a few milliseconds. However, when no battery or an abnormal batterysuch as shorted batteries is connected while the DC power source 5 isconnected, the voltage rapidly decreases as illustrated by a dotted lineA even if the voltage of the battery terminal P5 is not less than thevoltage V1. Specifically, the voltage becomes less than the voltage V1(almost 0 V) within the waiting time T1. Therefore, when the firstvoltage detection signal S1 sent from the comparator 15 is on a lowlevel after the waiting time T1 in step S5, the controlling circuit 18judges that no battery or a shorted battery is connected, and inhibitscharging (in step S22). Even when the charging device is in the chargeinhibition state in step 22, the battery voltage checking operation instep S5 is performed. Therefore, when the battery voltage Vb becomes notless than the voltage V1 and the first voltage detection signal S1 sentfrom the comparator 15 is changed to a high level, charging is performedon the battery.

Next, the battery connection confirmation operation in transition fromthe preliminary charge mode operation to the first rapid charge modeoperation (i.e., a constant current charging mode operation) will beexplained.

During the preliminary charging is performed (step S6), the controllingcircuit 18 performs the operation in step S7, i.e., checks the batteryvoltage. When the battery voltage Vb becomes not less than the voltageV2, the second voltage detection signal S2 output from the comparator 17is changed from a low level to a high level, and the operation proceedsto step S8 (i.e., the first charge stop time T2). The first charge stoptime is represented as T2 in FIG. 3. In the first charge stop time T2,the controlling circuit 18 outputs a signal to stop the charge currentich to the charge current controlling circuit 12. The first charge stoptime T2 is an extremely short time on the order of a few milliseconds.When a normal battery is connected, the battery voltage Vb hardlychanges in the first charge stop time T2 as illustrated by a solid linein FIG. 3.

When the battery 6 is removed from the charging device in thepreliminary charging operation, the voltage at the battery connectionterminal P5 rapidly increases to the second voltage V2 as illustrated bya dotted line B, and thereby the second voltage detection signal S2 fromthe comparator 16 is changed to a low level to a high level. However, inthis case, application of the charge current ich is stopped, the voltageat the battery connection terminal P5 rapidly decreases so as to belower than the voltage V2−, which is obtained by subtracting thehysteresis voltage of the comparator 16 from the second voltage V2 asillustrated by a dotted line B′. Therefore, the second voltage detectionsignal S2 from the comparator 16 is changed to a high level to a lowlevel.

In the first charge stop time T2, the controlling circuit 18 checks thebattery voltage (step S9). When the battery voltage Vb is not less thanthe voltage V2− and the second voltage detection signal S2 from thecomparator 16 maintains the high level, the operation proceeds to step10, i.e., the first rapid charge mode operation is performed.

In the first rapid charge mode operation, the battery 6 is subjected toconstant current charging applying a large amount of current so as to berapidly charged. In FIG. 3, the charge current in the first rapid chargemode operation is represented as i3.

As mentioned above, in a case where the battery is removed from thecharging device, the battery voltage Vb becomes less than the voltageV2− in step S-9 and the second voltage detection signal S2 is changed toa low level. In this case, the controlling device 18 judges that thereis no battery, and performs a predetermined abnormality detectionoperation (in step S23), e.g., the controlling device 18 allows thecharge current controlling circuit 12 to turn off the power transistorQ1 so that the power transistor achieves a shutoff state.

Next, the battery connection confirmation operation in transition fromthe first rapid charge mode operation to the second rapid charge mode(i.e., a constant voltage charge mode operation) will be explained.

During the controlling circuit 18 allows the power transistor Q1 toperform the first rapid charge mode operation via the charge currentcontrolling circuit 12 (step 10), the controlling circuit 18 alwayschecks the battery voltage Vb (step 11). When the battery voltage Vb isnot less than the third voltage V3, the third voltage detection signalS3 output from the comparator 17 is changed from a low level to a highlevel and the charging device has a second charge stop time T3, which isrepresented as T3 in FIG. 3.

In the second charge stop time T3, the controlling circuit 18 allows thecharge current controlling circuit 12 to stop application of the chargecurrent ich by the power transistor Q1. The second charge stop time T3is an extremely short time on the order of a few milliseconds. In thiscase, a normal battery is connected, the battery voltage Vb hardlychanges in the second charge stop time T3 as illustrated by a solid linein FIG. 3. However, when the battery 6 is removed from the chargingdevice in the first rapid charging operation, the voltage at the batteryterminal P5 rapidly increases as illustrated by a dotted line C in FIG.3. When the voltage reaches the voltage V3, the third voltage detectionsignal S3 from the comparator 17 is changed from a low level to a highlevel. In this case, when application of the charge current ich isstopped, the voltage at the battery terminal P5 rapidly decreases asillustrated by a dotted line C′. When the voltage at the batteryterminal P5 becomes lower than the voltage V3−, which is obtained bysubtracting the hysteresis voltage of the comparator 17 from the thirdvoltage, the third voltage detection signal S3 is changed from a highlevel to a low level.

Therefore, in the second charge stop time T3, the controlling circuit 18checks the battery voltage Vb (step 13). When it is found from the thirdvoltage detection signal S3 that the battery voltage Vb is not less thanthe voltage V3− in step S13, the second rapid charge mode operation(i.e., a constant voltage charging operation) in step S14 is performedon the battery. It is clear from the charge current curve in FIG. 3 thatthe charge current ich gradually decreases in the second rapid chargemode operation. In the second rapid charge mode operation, thecontrolling circuit 18 always checks the charge current ich on the basisof the output signal Si sent from the charge current detection circuit13 (step S15).

As mentioned above, in a case where the battery is removed from thecharging device in the first rapid charge mode operation, the batteryvoltage Vb becomes less than the voltage V3− in step 13 and the thirdvoltage detection signal S3 is changed to a low level, the controllingcircuit 18 determines that no battery is connected and the operationproceeds to step 23.

Next, the battery connection confirmation operation on completion ofcharging will be explained.

As mentioned above, the controlling circuit 18 always checks the chargecurrent ich in the second rapid charging mode in step 14. When thecharge current ich is less than a current i2 (i.e., a full chargecurrent) which is less than the current i3 in the first rapid chargemode operation and not less than the current i1 in the preliminarycharging, the charging device has a full charge waiting time T4, whichis represented as T4 in FIG. 3 and in which the charge current ich isstill applied to the battery.

The full charge waiting time T4 is an extremely short time on the orderof a few milliseconds. When a normal battery is connected, change of thecharge current ich in the full charge waiting time T4 is little asillustrated by a solid line in FIG. 3.

However, when the battery is removed from the charging device in thesecond rapid charge mode operation, the charge current ich rapidlydecreases so as to be less than the current i1 in the preliminarycharging as illustrated by a dotted line D in FIG. 3. When the chargecurrent ich is not less than the current i1 and less than the current i2in the full charge waiting time T4, the controlling circuit 18determines that the battery is fully charged and the operation proceedsto step 18 (i.e., the charging operation is ended). When the chargecurrent ich becomes lower than the current i1 in the full charge waitingtime T4, the controlling circuit determines that no battery isconnected, and the operation proceeds to step 23.

Next, connection confirmation operation in the beginning of re-chargingwill be explained.

The controlling circuit 18 checks the battery voltage Vb (step 19) evenat the end of charging (step 18). When the battery voltage Vb becomeslower than the voltage V3−, which is obtained by subtracting thehysteresis voltage of the comparator 17 from the third voltage V3, thethird voltage detection signal S3 from the comparator 17 is changed to alow level, and thereby the charging device has a re-charge start waitingtime T5 (step S20), which is represented as T5 in FIG. 3 and in whichthe charge current ich is not applied. Since the re-charge start waitingtime T5 is an extremely short time on the order of a few milliseconds,change of the battery voltage is little in the re-charge start waitingtime T5 if a normal battery 6 is connected as illustrated by a solidline in FIG. 3. However, when the battery is removed from the chargingdevice at the end of charging, the battery voltage Vb rapidly decreasesas illustrated by a dotted line E in FIG. 3 and the second voltagedetection signal S2 from the comparator 16 or the first voltagedetection signal S1 from the comparator 15 is changed to a low level.

Therefore, the controlling circuit 18 checks the battery voltage Vb inthe re-charge start waiting time T5. When the second voltage detectionsignal S2 from the comparator 16 is on a high level, the controllingcircuit 18 judges that the battery voltage Vb decreases while thebattery is still connected and the operation in step S10 is re-executed(i.e., the constant current charging operation is performed). When thesecond voltage detection signal S2 from the comparator 16 is on a lowlevel or the first voltage detection signal S1 from the comparator 15 ison a low level, the controlling circuit 18 judges that the battery 6 isremoved therefrom or the battery has a short-circuit state, and theoperation proceeds to step S22. In addition, when the third voltagedetection signal S3 is on a high level, the operation returns to stepS18, in which the controlling circuit 18 checks again the batteryvoltage Vb.

In determination whether the battery is connected in the beginning ofre-charging, whether to use the output signal from the comparator 15 orthe output signal from the comparator 16 is determined while consideringthe relationship between the re-charge start waiting time T5 and thevoltage dropping speed at the battery connection terminal P5 when thebattery is removed. Specifically, when the voltage at the terminal P5gradually decreases or the re-charge start waiting time T5 is so shortthat it is not expected that the voltage at the terminal P5 reaches thesecond voltage V2 in the re-charge start waiting time, the secondvoltage detection signal S2 from the comparator 16 should be usedtherefor. In contrast, when it is not expected that the voltage at theterminal P5 reaches the first voltage V1 in the re-charge start waitingtime T5, the first voltage detection signal S1 from the comparator 15should be used therefor.

Thus, in the first example embodiment of the charging device of thepresent invention, the voltage at the battery connection terminal P5 orthe charge current ich is checked at the five waiting/stop times T1-T5to determine whether a battery is connected. Therefore, it is notnecessary to perform intermittent charging and it is possible to chargean over-discharge battery. In conventional charging devices, thewaiting/stop times have been used for confirming change of the chargingmodes. In addition, the voltages and currents, which are used forjudging connection of a battery in the present invention, have beenmeasured for judging whether the charging mode is changed inconventional constant current-constant voltage charging methods.Therefore, only by substituting some of the conventional comparatorswith hysteresis comparators, connection of a secondary battery can beconfirmed. Therefore, problems such as increase in size of the chargingdevice and increase in manufacturing costs can be avoided.

Further, the hysteresis voltages of the comparators 16 and 17 can be setto desired voltages by the control signals from the controlling circuit18. Specifically, the hysteresis voltages should be set to propervoltages in consideration of the battery to be charged, and the chargingconditions such as charge current. Therefore, this charging device canbe used for charging various secondary batteries.

Furthermore, if it is not necessarily perform the battery connectionconfirmation operation at each of the waiting/stop times T1-T5, it ispossible to perform a battery connection confirmation operation atdesired points of the waiting/stop times T1-T5. In addition, it ispossible to form all the battery connection confirmation programs orsome of the battery connection confirmation programs in the IC in whichthe charge controlling circuit 2 is formed. In this case, selection ofthe connection confirmation method suitable for the application isperformed in the manufacturing process of the IC, for example, by usinga method such as cutting a trimming fuse.

In addition, it is possible to properly set the first voltage V1, thesecond voltage V2, the third voltage V3, the first current i1, thesecond current i2, the third current i3, and the waiting/stop timesT1-T5 by a trimming method in the manufacturing process. By using thismanufacturing method, the resultant IC, which is constituted of only onekind of circuit, can be used for various charging applications.

Further, a terminal for external signals can be added to the charging ICso that the charging conditions and/or the connection confirmationconditions of the charging IC can be changed by an external signal. Byusing this method, the resultant IC can be used for various chargingapplications.

Second Example Embodiment

In the first example embodiment, the impedance between the batteryconnection terminal P5 and the ground terminal P6 is considerably high.Therefore, there is a large stray capacitance due to the wire connectingthe terminal P5 with the terminal P6, resulting occurrence of a problemin that a charge is stored in the stray capacitance, thereby generatinga voltage between the terminals P5 and P6. In general, the straycapacitance is very small and therefore the generated voltage isdischarged shortly. However, in the above-mentioned case where theimpedance is very large, a problem in that the generated voltage cannotbe discharged in a waiting/stop time may occur. Therefore, it ispreferable to turn on a current load 20 (illustrated in FIG. 4) in thewaiting/stop times T1, T2, T3 and T5 to discharge the charges stored inthe stray capacitance. In this case, connection of the battery 6 can bedetected more securely. Next, the second example embodiment will beexplained by reference to drawings.

FIG. 4 is a schematic view illustrating the second example embodiment ofthe charging device of the present invention. In FIGS. 1 and 4, likereference characters designate like corresponding parts. The explanationof the parts illustrated in FIG. 1 is omitted or briefly explained hereand the differences between the devices illustrated in FIGS. 1 and 4will be mainly explained.

The differences therebetween are as follows.

(1) The current load 20 is inserted between the battery connectionterminal P5 and the ground terminal P6; and

(2) An input terminal P7, through which an external signal is input tothe controlling circuit 18, is provided in the charge controllingcircuit 2.

Due to these differences, the charging device and the charge controllingcircuit illustrated in FIG. 4 have reference numerals 1 a and 2 a,respectively. The current load 20 serves as a current source.

In FIG. 4, the charging device 1 a includes the DC power source 5 (suchas AC adaptors), and charges the secondary battery 6 (such aslithium-ion batteries) by performing constant current charging orconstant voltage charging.

The charging device 1 a includes the power transistor Q1, the resistorR1, the diode D1, and the charge controlling circuit 2 a, which controlsthe power transistor Q1 so as to perform constant current charging orconstant voltage charging on the battery 6 on the basis of theinformation on the battery voltage Vb and the charge current ichobtained from the difference in voltage between the first and secondcharge current detection terminals P3 and P4.

The charge controlling circuit 2 a, which is integrated in oneintegrated circuit, includes the DC power connection terminal P1, thecharge control signal output terminal P2, the first current detectionterminal P3, the second current detection terminal P4, the batteryconnection terminal P5, the ground terminal P6, and the external signalinput terminal P7. An external signal Se such as sleep signals to allowthe load 7 to achieve a sleep state is input to the external signalinput terminal P7. In addition, the charge controlling circuit 2 aincludes the power voltage detection circuit 11, the charge currentcontrolling circuit 12, the charge current detection circuit 13, thereference voltage generation circuit 14, the comparators 15-17, theresistors R11-R14, the controlling circuit 18, and the current load 20which is subjected to drive control according to the control signal fromthe controlling circuit 18.

The current load 20 is inserted between the terminals P5 and P6, and thecontrol signal is input to the control terminal of the current load 20from the controlling circuit 18 to perform drive control on the currentload 20 according to the control signal. Upon reception of the externalsignal Se, the controlling circuit 18 turns on the current load 20 inthe waiting/stop times T1, T2, T3 and T5. In other periods, thecontrolling circuit 18 turns off the current load 20 independently ofthe external signal Se. When the current load 20 is turned on, apredetermined current flows through the current load 20. When thecurrent load 20 is turned off, the current load achieves a shutoffstate.

In this second example embodiment, when the external signal Se to allowthe load 7 to achieve a sleep state is input through the external signalinput terminal P7, the controlling circuit 18 turns on the current load20 in each of the waiting/stop times T1, T2, T3 and T5, and turns offthe current load 20 in other periods.

In general, the impedance between the battery terminal P5 and the groundterminal P6 in the charge controlling circuit 2 a is considerably high.In addition, there is a large stray capacitance due to the wireconnecting the terminal P5 with the terminal P6. Therefore, charges arestored in the stray capacitance, thereby generating a voltage betweenthe terminals P5 and P6. In general, the stray capacitance is very smalland therefore the generated voltage is discharged shortly. However, inthe above-mentioned case where the impedance is very large, there is apossibility that the generated voltage cannot be discharged in awaiting/stop time. Therefore, in this example embodiment, the currentload 20 (illustrated in FIG. 4) is turned on in each of the waiting/stoptimes T1, T2, T3 and T5 to discharge the charges stored in the straycapacity and to securely detect connection of the battery 6. The currentflown through the current load 20 due to discharging is from 0 to a fewmilliamp. It is preferable to determine the current (i.e., to choose aproper current) in the manufacturing process of the charging device inconsideration of the impedance and stray capacitance or to determine thecurrent by inputting an external signal from the external signal inputterminal P7. Upon reception of the external signal Se, the controllingcircuit 18 determines the effective (or ineffective) waiting/stop timesamong the waiting/stop times T1-T5; the current in the current load 20;and other targets such as the first to third voltages V1-V3, and firstto third currents i1-i3, and the period of the selected waiting/stoptimes.

FIG. 5 is a flowchart illustrating the operations of the charging deviceillustrated in FIG. 4. In FIGS. 2 and 5, like reference charactersdesignate like corresponding operations. The explanation of theoperations illustrated in FIG. 2 is omitted or briefly explained hereand the differences between the operations illustrated in FIGS. 2 and 5will be mainly explained. FIG. 3 can also be used for the chargingdevice illustrated in FIG. 4.

The differences therebetween are as follows.

(1) In the operations illustrated in FIG. 5, the current load is turnedon in each of steps S4 a, S8 a, S12 a and S20 a.

Specifically, in each of steps S4 a, S8 a, S12 a and S20 a, thecontrolling circuit 18 turns on the current load 20 upon reception ofthe external signal Se to allow the load 7 to achieve a sleep statethrough the external signal input terminal P7.

Thus, in this second example embodiment, the current load 20, which candischarge charges stored in the stray capacitance present between theterminals P5 and P6, is added to the charge controlling circuit of thefirst example embodiment of the charging device. Therefore, in additionto the effect of the first example embodiment charging device, thesecond example embodiment charging device has an advantage such thatconnection of a battery can be detected more securely. In addition, thecharging conditions and battery connection confirmation conditions canbe freely set by an external signal. Therefore, the charging device canbe used for various applications even though the charging device usesonly one kind of IC.

This document claims priority and contains subject matter related toJapanese Patent Application No. 2006-052699, filed on Feb. 28, 2006,incorporated herein by reference.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth therein.

1. An integrated circuit for charging a secondary battery via a chargingtransistor, comprising: a charge current detection circuit which detectsa charge current output from the charging transistor, and generates andoutputs a signal including the charge current information; a voltagecomparison circuit which compares a voltage of the secondary batterywith one or more predetermined voltages, and generates and outputs asignal including the voltage comparison information; and a chargecontrolling circuit which controls the charging transistor according toinformation on the voltage of the secondary battery and the signalsoutput from the charge current detection circuit and the voltagecomparison circuit such that the charging transistor performs constantcurrent charging in which a predetermined current is output or constantvoltage charging in which a charge current is output so that thesecondary battery has a predetermined voltage, wherein, when the voltagecomparison circuit detects that the voltage of the secondary batterybecomes not less than a predetermined voltage V2, the charge controllingcircuit stops applying a charge current for a predetermined time T2, andwherein, when the voltage comparison circuit detects that the voltage ofthe secondary battery becomes less than a predetermined voltage V2− lessthan the voltage V2 within the predetermined time T2, the chargecontrolling circuit judges that the secondary battery is abnormallyconnected and performs an abnormality correction treatment.
 2. Theintegrated circuit according to claim 1, wherein the voltage comparisoncircuit includes: a comparator which compares the voltage of thesecondary battery with the voltage V2 and generates and outputs a signalS2 including the comparison information to the charge controllingcircuit, wherein the comparator has a hysteresis controlled according toa control signal input from the charge controlling circuit, and whereinthe voltage V2− is a difference between the voltage V2 and thehysteresis.
 3. The integrated circuit according to claim 1, wherein,when the charge current detection circuit detects that the chargecurrent applied to the secondary battery becomes less than apredetermined current i2, and further detects that the charge currentbecomes less than a predetermined current i1 less than the current i2within a predetermined time T4, the charge controlling circuit judgesthat the secondary battery is abnormally connected and performs anabnormality correction treatment.
 4. The integrated circuit according toclaim 1, wherein: when the voltage comparison circuit detects that thevoltage of the secondary battery becomes not less than a predeterminedvoltage V3 greater than the voltage V2, the charge controlling circuitstops applying a charge current for a predetermined time T3, and whenthe voltage comparison circuit detects that the voltage of the secondarybattery becomes less than a predetermined voltage V3−, which is greaterthan the voltage V2 and less than the voltage V3, within thepredetermined time T3, the charge controlling circuit judges that thesecondary battery is abnormally connected and performs an abnormalitycorrection treatment.
 5. The integrated circuit according to claim 4,wherein the voltage comparison circuit includes: a first comparatorwhich compares the voltage of the secondary battery with the voltage V2and generates and outputs a first signal S2 including the comparisoninformation to the charge controlling circuit; and a second comparatorwhich compares the voltage of the secondary battery with the voltage V3and generates and outputs a second signal S3 including the comparisoninformation to the charge controlling circuit, wherein the first andsecond comparators have a first hysteresis and a second hysteresis,respectively, controlled according to control signals input from thecharge controlling circuit, and wherein the voltage V2− is a differencebetween the voltage V2 and the first hysteresis, and the voltage V3− isa difference between the voltage V3 and the second hysteresis.
 6. Theintegrated circuit according to claim 1, further comprising: an inputterminal which is connected with the secondary battery and to which thevoltage of the secondary battery is input; and a current source whichapplies a current while being controlled according to the controlsignals input from the charge controlling circuit, wherein the chargecontrolling circuit controls drive of the current source according to anexternal control signal for controlling a consumption current of a loadto which a power is applied from the secondary battery.
 7. Theintegrated circuit according to claim 6, wherein: the charge controllingcircuit allows the current source to operate when the external signal isa signal to reduce the consumption current is input while the chargecurrent is not supplied to the secondary battery, and when input of theexternal signal is stopped, the charge controlling circuit stops theoperation of the current source.
 8. The integrated circuit according toclaim 1, wherein, when the charge controlling circuit judges that thesecondary battery is abnormally connected, the charge controllingcircuit stops applying a charge current to the secondary battery.
 9. Acharging device for performing a constant current charging or a constantvoltage charging to a secondary battery comprising: a DC power sourceconfigured to apply a DC power to a charging transistor; the chargingtransistor configured to apply a charge current to the secondarybattery; and a charge controlling integrated circuit for controlling thecharging transistor according to the information on the charge currentapplied to the secondary battery and the voltage of the secondarybattery, wherein the charge controlling integrated circuit is theintegrated circuit according to claim
 1. 10. A method for detectingconnection of a secondary battery comprising: applying a charge currentto a secondary battery through a charging transistor; checking thevoltage of the secondary battery; stopping applying a charge current fora predetermined time T2 when the voltage of the secondary batterybecomes not less than a predetermined voltage V2; and performing anabnormality correction treatment when the voltage of the secondarybattery becomes less than a predetermined voltage V2− less than thevoltage V2 within the time T2.
 11. A method for detecting connection ofa secondary battery comprising: applying a charge current to a secondarybattery through a charging transistor; checking the voltage of thesecondary battery; stopping applying a charge current for apredetermined time T2 when the voltage of the secondary battery becomesnot less than a predetermined voltage V2; and performing an abnormalitycorrection treatment when the voltage of the secondary battery becomesless than a predetermined voltage V2− less than the voltage V2 withinthe time T2, wherein when the voltage of the secondary battery does notbecome less than the predetermined voltage V2 within the time T2, themethod further comprises: checking the charge current for apredetermined second time T4 when the charge current applied to thesecondary battery is less than a predetermined current i2; andperforming an abnormality correction treatment when the current is lessthan a predetermined current i1 less than the current i2 within the timeT4.
 12. The method according to claim 11, further comprising: stoppingthe charge current to the secondary battery for a predetermined time T3when the voltage of the secondary battery becomes not less than apredetermined voltage V3 before the charge current checking step; andperforming an abnormality correction treatment when the voltage becomesless than a predetermined voltage V3−, which is greater than the voltageV2 and less than the voltage V3 within the time T3.
 13. The methodaccording to claim 10, wherein the abnormality correction treatmentperforming step comprises: stopping applying a charge current to thesecondary battery.